who fouled whom?

[Doreen Rich]

No: HPFGUIDX 18641

I am not a sports fan, by any means. I read this part of GF and I am 
totally confused.

Shouldn't Slytherin get the penalty? Isn't Malfoy the one who 
committed the foul? It is a foul to grab another player's broomstick.

At the end, it says the Slytherins are delighted with Malfoy's foul 
on Harry... if this is the case, why did Gryffindor take the penalty?

Here is the quote from GF:

"Harry put on a huge burst of speed; the wind was roaring in
his ears; he stretched out his hand, but suddenly, the Firebolt
was slowing down --

    Horrified, he looked around. Malfoy had thrown himself forward,
grabbed hold of the Firebolt's tail, and was pulling it back.

    "You --"

    Harry was angry enough to hit Malfoy, but couldn't reach --
Malfoy was panting with the effort of holding onto the Firebolt,
but his eyes were sparkling maliciously. He had achieved what he'd
wanted to do -- the Snitch had disappeared again.

    "Penalty! Penalty to Gryffindor! I've never seen such
tactics." Madam Hooch screeched, shooting up to where Malfoy was
sliding back onto his Nimbus Two Thousand and One.

    "YOU CHEATING SCUM!" Lee Jordan was howling into the megaphone,
dancing out of Professor McGonagall's reach. "YOU FILTHY, CHEATING
B --"

    Professor McGonagall didn't even bother to tell him off.  She
was actually shaking her finger in Malfoy's direction, her hat had
fallen off, and she too was shouting furiously.

    Alicia took Gryffindor's penalty, but she was so angry she missed
by several feet. The Gryffindor team was losing concentration and
the Slytherins, delighted by Malfoy's foul on Harry, were being
spurred on to greater heights."